


Ocean Studies

by Dirtyglass, Yumehi



Category: Haikyuu!!
Genre: Alternate Universe - Canon Divergence, Alternate Universe - Fantasy, Catch us in hell part 2, F/M, Fluff and Smut, Multi, Non-Human Genitalia, Reader is science nerd, Reader-Insert, mermaid au, merman, merman dick
Language: English
Status: In-Progress
Published: 2017-01-03
Updated: 2017-01-06
Packaged: 2018-09-14 10:14:21
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,854
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9176485
Author URL: https://archiveofourown.org/users/Dirtyglass/pseuds/Dirtyglass, https://archiveofourown.org/users/Yumehi/pseuds/Yumehi
Summary: You've always had an intense love for the ocean and its creatures, including the fictitious ones. What happens when you meet a real life merman after years of studying oceanology?A reader insert involving various Haikyuu! guys as mermen.





	1. Prologue

Oceans and water had always been your passion for as long as you could remember. You had taken swimming lessons at five, joined the swim team middle school into your high school years, and majored in ocean biology all throughout college. You also went out of your way to visit every aquarium near and far. The ocean was your life passion, you just couldn’t learn enough about the endless body of water that was 70% of the earth. Following your lifelong passion was how you ended up in this small ocean side fishing community, living on your own in a small cottage right on the beach.

Rumors had long since been spread about merpeople existing around the world. Did you believe it? Well, considering how big the ocean is, there was a large chance they were around somewhere. Who were you to oppose the possibility? Plus if you could meet or even see one in person that would be good enough for you. Which is what brought you to this particular town, it was the nearest to home and the ocean, it also had the most rumors of merpeople sightings too.

Leading you to the pier, you sat on the edge of the boardwalk with your feet dangling in the water. It became nearly a daily ritual to go there everyday with a notebook and binoculars. Taking notes of which times they’d obviously wouldn't be there, and any other sort of idea that popped into your head. You’d also explore along the nearby beach, becoming the local merperson expert by the locals. You didn’t pay much attention to that, more focused on finding any evidence you could. You wanted more than anything to prove theories correct instead of the laughs people gave to you instead.

Another fruitless day went by, the locals once again mocking you behind your back as though you didn’t notice. You wouldn’t let it bother you, as frustrating as it was to grit your teeth and bare it.

As the sun began to set along the shoreline your feet began taking you to your favorite view in the small town, the pier. It was surprisingly large to accommodate the summer tourism and extended out fairly deep into the ocean waters. You had taken to sitting in the ledge of the wooden safety railings just so you could see the water just so. Taking a deep breath of ocean breeze you let sounds of the seagulls and water crashing against the shore over take you. You couldn’t help but smile remembering your fond memories of the beach and the first time your parents took you to see the ocean.

Moments passed as you watched the sun slowly set, the water being enveloped with fiery hues of the sun. Movement suddenly caught your eye, causing you to jump up and nearly fall of the pier, you were quick to right yourself as you grabbed your binoculars. 

Looking in the direction of the cove on the jutting peninsula you saw the movement again. It was a deep colored tail? A fish perhaps? You could barely tell it was there until… Wait! There is was again, that definitely was something coming from the cove.

You were sure of it, there was something happening at that cove, and it was more than a fish. There was one problem, you didn’t have any way of getting out there, and it was dark out. You cursed internally at the predicament, you wouldn't be able to explore it tonight. 

Your mind didn’t rest at all throughout the night, the image of the tail reflecting off the water stuck in your mind. You’d go out there first thing in the morning, and since you didn’t get a wink of sleep, you were greeted with the morning sun. 

The cove wasn’t a far swim from the looks of it, you could handle it from the years of swimming. The morning of your surprise expedition, you slipped on a one piece swimsuit and goggles and headed out to beach with nothing else. Not like you could carry anything else anyways, one of these days you really needed to purchase a boat.

The ocean water was freezing in the morning the moment you stuck your toes into it. A shiver went up your spine, yet with the image of the cove before you; you had to go on and prove those people wrong. Within moments you were taking off in a run down the beach with a smile on your face. Today would be a different day.

~~~

The swim to the cove took around twenty minutes, you were starting to feel the ache in your muscles around the ten minute mark. You knew there was no point in turning back, you’d have another 10 minute swim anyways. 

Arriving at the entrance of the cove, you grabbed onto a nearby rock to cling on and catch your breath. Looking around, there was nothing out of sorts, simply an empty cove. Swimming further inside you found a ledge to sit on and hoisted yourself onto.

Water reflected off the cave wall, it was hypnotizing to watch, the cave itself wasn’t very deep, you could easily see the other side of it. You pulled yourself out of the water and sat on the soft white sand, that was untouched for who knew how long. You drew your knees to your chest and watched the light dancing along the cave wall. The cave itself wasn’t scary by any means, the entrance was wide and gaping, the sun shone in gave it a comfortable feeling, but the upper part of the cave still provided enough shade and shelter that it was comfortable. Not too hot nor too cold.

A yawn suddenly overtook you and the feeling of exhaustion interrupted your observations. The swim had taken more out of you than you expected. You hadn’t been swimming as much as you used to. Another yawn escaped you and suddenly the idea of lying in the sand didn’t seem too bad. Before you knew it, you were lying back of the softest bed of sand and fast asleep, the ocean waves singing you a lullaby as your mind drifted off.


	2. Daichi

He smoothly moved through the water, going between rocks and moving on pure instinct towards the cove. It was Daichi’s secret spot to relax when he needed a break from the other merpeople that had the tendency to drain his patience. A particular orange haired merman was the cause of today’s stress. He’d come to close to a shark and began a long chase which Daichi had to break up. 

Bringing him to the cave, there was something off when he noticed a human--a woman, at that-- swimming to it. There was a time he was nearly spotted by this person, she had a tendency to stick around the pier for hours at a time. He couldn't make it to the cove as easily on those days without being spotted. He did his best to keep hidden, but it seemed he was finally spotted for good yesterday when he left. He had flipped his tail out of the water to avoid swimming into a school of fish. It seemed the woman had managed to notice that one moment and grabbed onto it. 

Today, Daichi stayed low to the surface floor, hoping to be deep enough out of her sight when he approached the cove. It seemed to work at first but this human was definitely a curious one.

Slithering to the top of the water, he peeked his head out of the water to see her on the small beach with her eyes closed… Was she alive? His heart fell to the bottom of his stomach at the thought. Even if she was a human, he didn’t wish her death or harm; especially one who hadn’t done anything bad to him. 

Daichi ducked underneath the water and swam to the shore, dragging himself up to the sand. He observed her figure at first, never once had he come this close to a human. He found himself staring at her legs, they were soft in appearance and looked smooth to the touch. He did find himself wondering what a human’s skin felt like. It was so very different from what he has, a shiny tail that could be described as slimy to some. 

Before the merman knew it, he was dragging his fingers up the length of your leg. He was completely entranced by the feeling grazing his fingertips. Then he remembered why he was here, to see if you were still alive! From what he heard from Sugawara told him that humans weren’t too different from merpeople. He assumed humans had a heart in the same area as you did. 

He lifted himself further onto the sand, one hand rested on your shoulder as he leaned his head over to your chest. Placing his ear against you, he was relieved to hear the sound of your heart beating at a normal pace. A sigh of relief passed through his lips

“Are you… real?” Daichi heard a soft voice ask.

You always were a light sleeper, you awoke the moment you heard splashing other than the waves against the beach you lied on. You kept your eyes closed and breathing soft and steady as you strained to listen to the sounds of something or in this case someone dragging themselves towards you. You had always been a woman of science and facts so the thought of it being a monster of some sort barely crossed your mind. 

What surprised you the most was the soft breathing and the warm very human hand touching your shoulder. No longer being able to contain your excitement you opened your eyes taking in the sight of a man, with short, deep black hair and dark skin, resting his head against your chest. The next thing your eyes took in was the long, shiny and thick tail attached to his torso. The tanned skin slowly gave way to deep green scales that formed, what was undeniably a fish tail. This had to be a dream…

Daichi lifted his head off her chest to see bright eyes staring down at him. So she really wasn’t dead, even better, she knew that merpeople were now real. This wouldn't be good, he should try leave before anymore questions could be asked. He started to turn around, yet--was stopped by your hand on his arm.

“Don’t go,” you spoke in a firm voice. “I have questions to ask!”

Daichi’s eyes opened wide at that remark, he should _really_ try to get out of here. Sugawara always warned him not to get close to humans. “I-I have to go?” he said more as a question. 

“No, no, no, just let me ask you a few things then you can go! I promise I won’t do any harm to you,” you spoke openly, tugging a bit harder on his arm. “Or tell anyone!” you added. 

You had to admit for a merman, he was incredibly attractive. He had the most gorgeous eyes and body to add. “Fine,” his voice was incredibly deep too, you felt a shiver run down your spine. “Not for long, though.” his tail swished around in the water as a nervous tick. 

“You’re gorgeous,” you spat out suddenly. “I mean, that’s not what I wanted to ask! I wanted to ask if I can touch your tail.”

“I, thank you?” he said, considering that he’d touch you earlier, it was only fair to return the favour. “Yes, you may.”

Your heart could have lept out of chest at his answer. All this time you knew that merpeople existed, in contrast you made a promise not to tell. But when that time came that you could; you’d let the towns people know that you weren’t wrong. There was a merman right before you, and he was letting you _touch_ his tail.

Raising your hand, you gingerly set your fingers on top of his scales. The incredibly smooth scales where your hand could nearly slip off. The color of his tail was breathtaking as well, never before had you seen a shade of green so rich in hue. You ran your hand down the length of his tail, moving to scoot further into the water and towards his fin. A nearly child like smile was glued to your face all the while. 

Daichi on the other hand was a bundle of nerves, never had he been this close to a human. He was warned not to be seen nor go near them as a safeguard to the mermaid community. This would get him in trouble, and still he remained. Maybe it was his gut telling him there was nothing to be afraid of with this human. She didn’t have any sort of weapon with her besides her sharp curiosity. 

He found himself staring at her legs, so unlike his own lower body of course. Separated, was one way of putting it. He’d only seen from afar a human’s legs, so this was an experience all to its own. Your hand on him certainly didn’t feel bad either, he could fall asleep with that caressing his tail. Wait, what was he thinking? He shouldn’t see this human after this surprise run-in, or come back to this cove either. 

“Thank you,” you said at last and took your hand off of him. “Your tail is amazing, I always knew merpeople existed and you’ve proven me correctly!”

“We try to keep ourselves hidden as you know. I trust that you’ll keep this a secret between us after we part our ways.”

“I won’t tell a soul,” you responded, a sudden though hitting you smack in the head. “Can we meet again, please? I don’t even know your name but I have so many questions to ask and I could keep you here all day if that were an option,” words spilling out like water. “I probably sound weird, don’t I?”

It took him a moment to process all of what you said before he found himself nodding his head. “A little, yes. I’ll agree to coming back one more time so you can ask your questions.” he started to say. “I have to admit, I’m interested in humans too, so you’ll have to be prepared.”

“And I’ll be ready to answer any of yours,” you said in response. 

~~~

After many more meetings you both began to realize you had a lot more in common than you had ever thought. Before you knew it your interactions had started to become a bit on the flirty side and both you and Daichi began looking forward to spending your days together.

As expected, your questions would reach more intimate areas of each other’s lives. You asked him of family, his life, and his friends. He’d go into tangents about different members of his group. One being an orange haired merman who had the energy of five merman. Another one with jet black hair who’d constantly yell at him. They were certainly an odd ball duo as he described.   
It made you think of the beginning of your first meeting, he’d only promise to stick around for two meetings tops. Now you two were meeting nearly every other day, at least, when you could swim out there without people noticing. 

Today in particular, you asked Daichi if he could explain more about of the physiology of his body. It taken weeks to gain the courage to ask this, but it was burning in the back of your mind before you even meet him. 

“Daichi, I know this will be weird to ask,” you began, kicking your feet in the water slowly. 

“What is it?” he was on his back, floating in the water while looking up at the cave of the ceiling. 

“What does your reproductive organ look like?”

“My what?” he said, sitting up in the water to look at you better. 

“Your, you know… What merpeople use to make little merchildren?”

“You want to know about that?” he sprung up out of the water next to you. “Why?”

A slight blush began to come over your face, but you had to know. All this waiting wasn’t going to go to waste. “I’m curious, okay? You can say no if you want to.”

The thought of having to show her that began to awaken something inside of Daichi. He could already feel himself start to harden at the thought. “No I can do it, just, don’t make it weird since I know that’s a trait of yours,” he started to smile at you. 

“Hush you!”

~~~

“So that’s how it works,” the inner scientist in you was fascinated by his cock. It came out from a slit when erected, though it didn’t look far from a human’s own. Interesting to you, you’d have to take note of this when you swam back home.

Though it was obvious that Daichi was more than embarrassed. He was leaned back on his forearms on the beach, covering his face with one hand. “Y-Yeah, I think you get the idea now,” he stuttered out, how did he let it come to this? It was obvious he had a small affection for you, that soon became the answer to his question. “I’ll just--put this away now...”

“Wait!” you stopped him. “How does mating or reproduction work?”

“Mating?!” he sputtered, dragging his hand down his face. The color of his face was bright red at this point. He knew you were a scientist, but he didn’t think you’d be going _this_ far with your questioning. “You meet someone important to you and then… Then stuff happens!” he managed. 

“How, Daichi? You know I need details, I’m not going to miss out on this chance to learn!” 

“The same as humans, I suppose? Don’t human woman have, well, something similar to what mermaids have?” he avoided the question as much as possible. 

“I imagine so now that I’ve seen your...” you looked down at his cock, “... That. We’re probably similar. Wait, have you mated with a mermaid?! We can do a comparison of our reproductive organs!”

Daichi’s cheek’s flared up into a completely new shade of pink at your suggestion. “No, I haven’t mated with anyone! That’s a personal question anyways!” He could feel the blush reach the tip of his ears. What was worse, the situation was starting to settle in. He was alone with someone he has feelings for. 

And there was also the plain fact that he still had an erection despite all the conversation happening. _Oh no,_ he thought to himself. _Think of something else, think of something else_. Yet none of that help when you were in a form fitting one piece with water dripping down your smooth skin. There he was, most definitely staring at her like a creep.

“I was only asking, Daichi.” you began, fixing the strap of your swimsuit. “You’re awfully on edge today from what I’ve seen.” you moved to place a hand on his forehead. His eyebrows rose up, big brown eyes staring right back at you. “You know… You can put that away now,” you started to smirk at him. 

“I-I… Can’t,” he muttered under his breath, today couldn't get anymore embarrassing. “You being around isn’t helping, I’ll can go swim it off,” Daichi couldn't look you in the eyes any longer after showing you his reproductive organ. 

“Me? So you’re saying I’m a distraction,” you began to scoot closer to him. 

“Well, I mean, yes, you are!” Daichi gaped, a muscular arm scratching the back of his head out of nervousness. “You’re a very gorgeous human and we’ve been talking for a while now. It doesn’t help that you’re around when I have this thing up,” now came the word vomit. 

“ _Oh_ ,” the word fell from your lips as a surprise to his confession. 

A blush creeped over your face as the realization of the situation hit you. All the things you had mentioned replayed in your head. You almost wanted to run away in embarrassment, but your eyes started to wander down from his pretty chocolate eyes, to his toned neck, tan broad shoulders all the way down his muscled chest and abs. You couldn’t stop the next few words that spilled out of your mouth “W-well… I can help with it, if you’d like.” You eyes glued to his straining erection.

It was definitely inhuman, you could easily tell by the way it stood from the slit in the center of his tail, where his torso ended and fishtail began. It was flesh tone but also had bits of color wrapped in it that matched his scales. What made it the most inhuman looking, was the fact that his cock had dull ridges going up either side of it along the pulsing veins. It gave way to the head that resembled a human glans. 

You found yourself licking your lips…

Daichi softly called out your name, blushing as he watched your eyes trace over his body. He wanted to say more but his already excited nature was starting to go to his head, as he watched droplets of water drip down your neck and disappear into your tight swimsuit.

“Touch me… Please.” He let out his tone deep and husky, doing nothing to mask his excitement. He found himself aching hard for some form of touch on his straining length. Anything to gain relief after how long he was keeping it up.

“Yes… Let me move first,” moving to straddle over his tail. His hardness pressed to the side of your thigh, twitching the moment your leg brushed over it. You wrapped your hand around the base of his cock, idly starting to stroke him over. You heard what sounded like a curse escape from his lips after a few ghost touches. But it was certainly enough to get you going. 

You glanced up to se Daichi’s eyes already glazed over with heat, he was into this already. You leaned over and caught him off guard, pressing kisses up the line of his throat. Though you did put one onto the gills on the side of his neck. A shaky breath left his lips, leaning his head back out of pure reaction. That seemed to be a special spot for the merman.

As a scientist, you were going to exploit this new found information. The sensitive gills were moving faster as Daichi took shorter breaths, his tail was still in the water as expected. Though the water was the least of his worry when there was a human straddling his lap. “Y-you seem to know what you’re doing,” he exhaled. 

“You’re not too different from a human’s build. Doesn’t take too much to get you into the mood considering this is your first time.”

“Hush--Fuck,” his frown turned into another curse and you began to pump him harder. His cock had more natural lubrication as beads of cum started to form at the tip. Gliding down in pearly strings onto your hand. 

“What were you saying?” you smiled at the merman before you, your lips pressed to the shell of his ear. 

“You’re fucking beautiful….” Daichi breathed out, as his hands caressed your thighs gently, as if asking permission to touch you. He couldn’t get enough of your soft flesh under his scaled hands, and his cock twitched in your hand in response.

A blush took over your cheeks this time, not expecting him to say something like that so suddenly. You had a fairly solid idea of what he was like, but the fact that he surprised you like he did just made him that more attractive.

“You can touch me too, Daichi.”

He looked you in the eyes, and your breath left you at the pure lust that you found staring back at you. The merman’s hand trailed up your back and threaded through your soft locks as he pulled you into a deep kiss. The kiss caught you off guard as Daichi gently pushed you back onto the soft beach sands. He pinned you between his muscled arms, his cock, rubbing against your inner thigh and covered heat, causing a small moan to escape you.

“You either tell me to stop now, or I won’t be able to later.” Daichi whispered into your ear, licking the sensitive flesh, causing a shiver to run down your spine. He went back to returning the favour of kissing down your neck. His teeth peeking out so he could nibble on the sensitive flesh. 

“Keep going,” you said back to him. 

“Are you sure?” he asked again.

“Yes!” you assured him, a bit on edge now that you were so close to doing this with him. Daichi moved down a hand down your side, placing it between your legs to move the strip of swimsuit covering you up away. It was even more different now being with a human--not that he was with a mermaid even to begin with. Still, there was the species difference. 

Without anymore warnings needed, Daichi pressed his hips forward, slipping easily into your pussy. You let out a low groan as he started to press further into you, the feeling different than anything else you had experienced before. Suddenly he thrusted forward into you, a feeling of pleasure bubbling in his stomach. “S-sorry,” he murmured, letting his head rest in the crock of your neck. “I’m a little excited,” he laughed against your skin. 

A small laugh came from you, adjusting your legs to wrap around his fit waist. “I don’t mind it a bit rough,” you responded, urging him forward by tightening your legs. Your head moved forward to plant a salty kiss onto his lips. He smelled of the sea and sunshine, and you were ready to drink in his scent. 

A smile graced his face, the corner of it wrinkling his eyes with it. “As you wish…” grinding in a slow rhythm into your core. The slow burn starting to build in your stomach as each of his movement grew more intense. The swish of water hit the back of your thighs at a particular hard thrust. By now he was entirely sheathed into you, enjoying the warmth you had to offer. 

“Daichi, keep going.” you urged forward, raising your hips to guide him further and get a deeper thrust into you. He grunted in response, using his hands on your waist to press deeper, harder. You leaned over to kiss along his sensitive gills as you leaned more about hi body. By his hips were the skin and scales meet were an especially sensitive. You heard small sounds of pleasure leave his throat when your hands brushed over the spot. 

“So, are you learning a lot?” he teased up at you.

“Mm… Plenty,” sitting all the way back on his cock, the stretch of it causing a new wave of sensation to go up your spine and cause goosebumps. Raising your hips and repeating the motion over and over until you were left panting and stretched loose. Daichi’s mouth was left open, your name written in breathless moans. 

Your hands reached over to his chest, sensually rubbing the thick muscles in a circle. Daichi’s expression flickered for a moment, this was definitely a new feeling to him. Though he wasn’t going to stop you, despite a chuckle that happened to escape his lips. “I thought I was suppose to be the one touching you there.”

“Sit back and enjoy yourself, merboy,” you said.

You name left his lips in a breathless sigh as his grip tightened on your hips, his thrusts becoming more desperate and erratic. The ridges on his shaft rubbed you inner walls harder causing you to cry out loud. The head of his cock hit your g-spot with a particularly hard cant of his hips. Your walls squeezed and undulated hard as your orgasm suddenly blindsided you. Daichi groaned louder and cried out in sync with you as his release coated your insides, hot and deep.

You were left keening in slow, steady thrusts until your orgasm was completely ridden out. While a certain Merman was covered in a sheen of sweat, oddly beautiful to look at the longer you stared at his chiseled appearance. Though you could feel him growing softer inside of you, and decided to get off him. 

In a sudden movement, you were on your back once again and Daichi was above you. A charming smile which could sway you any day and anywhere. “Thank you,” he spoke in whisper, moving to kiss your lips in an all too sweet manner. 

“Thank you for letting me learn a thing or two about Merman physiology,” a soft laugh coming from you after you returned the kiss.

“Promise this wouldn’t be the last time we meet?” he asked.

“I promise, if you’re willing to put up with more weird questions.”

“For you, I think I’ll be able to handle it.”

**Notes for the Chapter:**

> Hope you enjoyed this first character with the lovely Daichi ~Dirtyglass  
> DAICHI IS DADDY AS FUCK AND I LOVE HIM.... Thank you for reading everyone. ~Yumehi
> 
> Comments and Kudos are always loved <3

**Author's Note:**

> Here's another smutty fic by yours truly and Dirtyglass. 
> 
> We are accepting votes on who you'd like to see next, we're starting out with most of the captains. So far the choices are Bokuto, Kuroo, and Oikawa. Comment below to vote! Favorites, Comments, and Kudos are appreciated.


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